UNSET FUNCTION IN PHP

UNSET

Use : It Unset a given variable

But is this enough? I think it behaves more than that, depends on how and with respect to what you are using this function.For example you are destroying the local variable, global variable, static variable, or as a casting function. we will discuss later about the all given examples

HOW TO USE THIS

SYNTAX

void unset ($var1 [,$var2, ... ] )

unset is the function which will unset your variable.

$var1, $var2, ... are the variables which you wants to destroy. you can give any number of variables to destroy.

Return value: 

 It return nothing

BEHAVIOR OF UNSET FUNCTION 

The behavior of unset() function depends on what type of variable you are attempting to destroy.

Three types of variable you want to destroy

1.GLOBAL VARIABLE

If a GLOBAL variable is unset() inside of a function, only the local variable is destroyed not the GLOBAL variable. The GLOBAL variable inside the function will retain the same value as before unset() was called.

Let's discuss it with the help of an example

EXAMPLE

<?php
function destroyMe() 
{
    global $var;
    unset($var);
}

$foo = 'bar';//global variable
destroyMe();
echo $foo;
?>

OUTPUT

bar


The above function will only destroy the local variable
If you want to destroy global variable the you have do like this 

<?php

function desctroyMe() 

{

    unset($GLOBALS['var']);

}

$var = "destroyME";

echo "Before destroy value is:".$var;

desctroyMe();

echo "After destroy value is:".$var;

?>

OUTPUT

Before destroy value is:destroyME 

PHP Notice:  Undefined variable: var in /home/tarun/temp.php on line 11

After destroy value is:


2. LOCAL VARIABLE


If you want to destroy the local variable then just use the function unset($var).
We will not discuss about this in detail because its easy to do, just try yourself.

3. STATIC VARIABLE

<?php
function unsetMe()
{
   static $a;
   $a++;
   echo "Before unset a value is-->$a\n";
   unset($a);
   echo "$a\n";
   static $a;
   echo "After Unset a value is-->$a\n";

}


unsetMe();
unsetMe();
unsetMe();
?>


OUTPUT

PHP version  PHP 5.5.9-1

Before unset a value is-->1
PHP Notice:  Undefined variable: a in /home/tarun/temp.php on line 8

After Unset a value is-->1
Before unset a value is-->2
PHP Notice:  Undefined variable: a in /home/tarun/temp.php on line 8

After Unset a value is-->2
Before unset a value is-->3
PHP Notice:  Undefined variable: a in /home/tarun/temp.php on line 8

After Unset a value is-->3

You can see in the example that after unset is is again referencing to the same variable. surprised?. Yes it happen so when you will destroy the static variable, only refernece is destroyed to that variable, not the value.

Thats why when you have again get the reference using statement after unset

static $a;

It has linked you to the address of the variable, and printing the value of variable a.


4. AS A CASTING FUNCTION 

When you are using unset() as a casting function then it will now originally destroy the value of the variable. here is the expaple which will described everything. 

<?php
$name = 'Tarun';

var_dump((unset) $name);
var_dump($Tarun);
?>

OUPUT

NULL
string(5) "Tarun"



USEFUL LINKS

You can try here online

http://www.w3resource.com/php/function-reference/unset.php

Know how it behaves with array

http://stackoverflow.com/questions/6376702/php-unset-array-value